The Ngoi Chi Formation in the Phan Si Pan Area of Northwest Vietnam Revealed by Zircon U-Pb Age and Hf Isotope Composition
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摘要: 本文对越南西北部Phan Si Pan地区变质地体中的一个Ngoi Chi片麻岩进行了锆石CL内部结构分析、LA-(MC)-ICP-MS锆石U-Pb定年和Hf同位素分析。CL图象和Th/U比值特征显示该片麻岩样品中的锆石主要为岩浆锆石,有少量窄的变质边。岩浆锆石的年龄为~2.9 Ga,表明该样品是越南西北部Phan Si Pan地区的基底岩石。它们的εHf(t)值为–4.70±0.92,二阶段Hf模式年龄为~3.5 Ga,表明其为更古老的(>3.5 Ga)冥太古代地壳物质部分熔融作用形成。变质边部锆石给出了~1.8 Ga的年龄,表明变质作用发生在古元古代早期, Phan Si Pan地区在这一时期可能经历了一次重要的构造热事件。
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关键词:
- Vietnam /
- Phan Si Pan /
- U-Pb锆石 /
- Hf同位素 /
- 古老岩石
Abstract: This paper reports the result of an integrated study of zircon U-Pb age and Hf isotope composition for a gneiss sample (Ngoi Chi formation) from the Phan Si Pan area in northwest Vietnam. CL imaging reveals that most zircons are magmatic, with a few of them exhibiting thin metamorphic rims. The magmatic zircons gave a weighted mean U-Pb age of ~2.9 Ga, indicating the gneiss is the basement rock in the Phan Si Pan area. They haveεHf(t) value of –4.70±0.92, and two-stage Hf model age of ~3.5 Ga, indicating that the gneiss was derived from partial melting of >3.5 Ga crustal rock. The metamorphic rims yielded an age of ~1.8 Ga, implying that the metamorphic event occurred in the Neoarchean era, which might have been also a major tectono-thermal event in the Phan Si Pan area.-
Key words:
- Vietnam /
- Phan Si Pan /
- U-Pb zircon /
- Hf isotope composition /
- basement rock
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